312 GENUS ATRIPLEX. 



RELATIONSHIPS. 



This species and A. matamorensis constitute a small natural group, the relationships of 

 which are not known. It seems that they have been long separated from the more prim- 

 itive species and that they have not given rise to the more modern ones. The superior 

 radicle, together with the dioecious habit, is suggestive of a starting-point for the large 

 group of dioecious perennial species, but there is no direct connection with any of these. 

 Moreover, the dioecious true shrubs can be more logically connected with the monoecious 

 herbs through the pentandra-barclayana line, or it is not impossible that they have had 

 an origin entirely independent of any of the present North American species. 



A. decumbens and A. matamorensis possess certain features not present in any species 

 that they resemble in other characters. The opposite leaves are noteworthy in this 

 connection. Especially unique is the dilation of the pericarp around the thickened 

 bases of the stigmas. It is such considerations that lead to the assembling of these two 

 species into a single close group, notwithstanding their rather wide geographic separation. 



Constancy in all essential characters is a feature of A. decumbens. The only notable 

 exception, aside from the usual variation in the size of the fruiting bracts, is the presence 

 of rather well-marked forms differing in the size of the leaf. The type specimen is from 

 an average robust plant, the largest leaves measuring 1.5 cm. long by 1 cm. wide. In an 

 extremely large-leaved form the leaves measure 3.5 cm. long by 1.4 cm. wide and in this 

 the staminate inflorescence also reaches the maximum length of 10 cm. (Santa Barbara, 

 Bingham, Gr). The opposite extreme is a form with crowded subimbricate leaves only 

 0.8 to 1.2 cm. long by 0.3 to 0.6 cm. wide. This comes from San Clemente Island (August 

 25, 1894, Brandegee, UC) and from the mainland at National City {Hall 11214, UC). 

 Since these various forms can not be correlated with geographic distribution, and since 

 there is evidence of partial intergradation, it is believed that they are ecads. 

 ECOLOGY AND USES. 



Atriplex decumbens regularly forms dense mats one to several feet in diameter, from 

 the back-strand, where it grows with Distichlis and Oenothera bistorta, to the adjacent 

 slopes of Stipa setigera and Avena fatua, where also occur A. semibaccata, Baeria chryso- 

 stoma, Layia platyglossa, Eschscholtzia, Platystemon, etc. It is distinctly halophytic, 

 but less so than A. leucophylla. The plants bloom from April to July or later. 



This species is grazed to a slight extent by cattle, though they find the associated A. 

 semibaccata much more succulent. 



34. ATRIPLEX MATAMORENSIS Nelson, Proc. Riol. Sec. Wash. 17:99, 1904. Plate 49. 



Erect or ascending perennial, woody toward the base, 2 to 4 dm. high; branches 

 rather slender, terete but irregular and often crooked, obscurely furfuraceous, the old 

 bark breaking apart and exfoliating ; leaves nearly all strictly opposite, sessile, lanceolate 

 from a broad base, crowded and often imbricate, obtuse at base, acute at apex, 0.2 to 

 0.5 cm. long, 0.1 to 0.3 cm. wide, entire, thick, gray with a dense scurf, soft, l-nerved; 

 flowers dioecious, the staminate not known, the pistillate solitary or several in axillary 

 glomerules, these in rigid leafy spikes; perianth wanting in the pistillate flowers; fruiting 

 bracts sessile, strongly compressed, united to the middle or above, nearly orbicular, obtuse 

 but sometimes with a short mucronate apex, 2.5 to 3 mm. long and wide, sharply and 

 evenly dentate nearly to the base, the sides not appendaged but strongly 1- or 3-nerved; 

 seed 1.2 mm. long, yellowish; radicle superior. Pericarp continued as a flat white 

 sheath around the bases of the stigmas. 



Southwestern Texas and Tamaulipas. Type locality, Rio Grande Valley, near Mata- 

 moras, Tamaulipas. Collections : Type collection, Matamoras to San Fernando, October, 

 1830, Berlandier 3201 (Gr, NY); Corpus Christi Bay, southwestern Texas, Palmer 1160 

 (Gr, US); vicinity of Corpus Christi, Texas, Rose 18086 (US). 



